The incidence and prevalence of fibromyalgia are higher in multiple sclerosis than the general population: A population-based study.

Objective: Fibromyalgia adversely affects quality of life, yet little is known of the epidemiology of this condition in MS. We aimed to validate and apply administrative case definitions for fibromyalgia in MS.

Methods: Using administrative health data we identified persons with MS and an age-, sex- and geographically-matched general population (GP) cohort. Case definitions for fibromyalgia were developed using ICD-9/10 codes, validated against medical records, and applied to evaluate the incidence and prevalence of fibromyalgia.

Results: The case definition for fibromyalgia with ≥5 hospital or physician claims in 3 years had a sensitivity of 60%, specificity of 98%, and agreed moderately with medical records (κ=0.48). In 2005, the age-standardized prevalence of fibromyalgia was 6.82% (95% CI: 5.91-7.72) in the MS population and 3.04% (95% CI: 2.77-3.32) in the GP. After adjustment for age, sex and year, the incidence of fibromyalgia was 44% higher in the MS than the GP (IRR 1.44; 95% CI: 1.01-2.07). The incidence of fibromyalgia increased slightly over time in both populations.

Conclusions: The incidence and prevalence of fibromyalgia are higher in the MS population than the general population. Fibromyalgia should be considered in the management of pain in persons with MS.